An understanding of the genetic pathways and environmental circumstances that give rise to phenotypic variation in behavior is important for human health, from the psychological, sociological and pharmacological perspectives. Variation in behavior also plays a central role in animal evolution: animals must utilize all senses and react appropriately in order to survive and procreate; and differences in sexual behavior within a species can lead to reproductive isolation and speciation. Most behaviors are quantitative traits; they exhibit continuous phenotypic variation, attributable to the joint segregation of multiple interacting genes (quantitative trait genes, QTGs) whose effects are sensitive to the environment. The long-term goal of this project is to understand the genetic basis of variation for quantitative traits in terms of phenotypic and molecular variation at individual QTGs, using Drosophila melanogaster as a model system. In the current project period, we propose to characterize the genetic architecture of two complex behaviors in Drosophila, mating behavior and locomotor reactivity. The immediate goals for this project period are: (1) To identify and characterize new candidate genes that affect these behaviors by screening for quantitative effects on behavior of P element insertional mutations; (2) To identify QTGs contributing to variation in behavior between two strains, using a combination of high resolution recombination mapping and complementation tests; and (3) To determine what candidate genes potentially contribute to naturally occurring variation in behaviors, and to linkage disequilibrium mapping to map the molecular polymorphisms (Quantitative Trait Nucleotides, QTNs) associated with naturally occurring variation in behavior at three of these candidate genes. Identification of new genes affecting Drosophila behaviors will enrich our understanding of the network of genetic interactions required to produce these complex traits.